Towards independent control of polar and azimuthal anchoring

TL;DR

This study combines simulation, experiment, and theory to demonstrate how patterned substrates can independently control the polar and azimuthal anchoring directions of nematic liquid crystals, revealing complex alignment behaviors.

Contribution

It introduces a comprehensive approach to independently manipulate nematic liquid crystal anchoring using patterned surfaces, with detailed analysis of alignment behaviors based on pattern shape and anchoring strength.

Findings

For strong anchoring, nematic aligns with the rectangle's long edge.

In weak anchoring, anchoring is degenerate between diagonals.

Bistability occurs between diagonal and edge alignment under certain conditions.

Abstract

Monte Carlo simulation, experiment and continuum theory are used to examine the anchoring exhibited by a nematic liquid crystal at a patterned substrate comprising a periodic array of rectangles that, respectively, promote vertical and planar alignment. It is shown that the easy axis and effective anchoring energy promoted by such surfaces can be readily controlled by adjusting the design of the pattern. The calculations reveal rich behavior: for strong anchoring, as exhibited by the simulated system, for rectangle ratios $\geq 2$ the nematic aligns in the direction of the long edge of the rectangles, the azimuthal anchoring coefficient changing with pattern shape. In weak anchoring scenarios, however, including our experimental systems, preferential anchoring is degenerate between the two rectangle diagonals. Bistability between diagonally-aligned and edge-aligned arrangement is predicted for intermediate combinations of anchoring coefficient and system length-scale.